Conventionally, a vane pump has been known, which includes: a housing including a substantially circular pump chamber; a rotor that rotates about a position eccentric with respect to a center of the pump chamber; a vane that is rotated by the rotor and that always partitions the pump chamber into a plurality of spaces; an oil supply passage that intermittently communicates with the pump chamber by the rotation of the rotor; an oil supply pipe that is connected to this oil supply passage to supply a lubricating oil from a hydraulic pump thereto; and a gas passage that makes the pump chamber and an outer space communicate with each other when the oil supply passage communicates with the pump chamber by the rotation of the rotor, wherein
the oil supply passage includes: a diameter direction oil supply hole provided at a shaft part of the rotor in a diameter direction thereof; and an axial direction oil supply groove that is provided in the housing to communicate with the pump chamber, and with which an opening of the diameter direction oil supply hole is made to intermittently overlappingly communicate by the rotation of the rotor, and wherein the gas passage includes: a diameter direction gas hole that is provided at the shaft part of the rotor in the diameter direction thereof to communicate with the oil supply passage; and an axial direction gas groove that is provided in the housing to communicate with the outer space, and with which an opening of the diameter direction gas hole is made to intermittently overlappingly communicate by the rotation of the rotor, and wherein the diameter direction gas hole is made to communicate with the axial direction gas groove when the diameter direction oil supply hole is made to communicate with the axial direction oil supply groove. (Patent Document 1)
In the above-described vane pump, when the rotor stops in a state where the diameter direction oil supply hole of the oil supply passage is in communication with the axial direction oil supply groove, the lubricating oil inside the oil supply passage is drawn into the pump chamber by a negative pressure thereinside. If a large amount of lubricating oil is then drawn into the pump chamber, an excessive load is added to the vanes when the vane pump is subsequently started in order to discharge the lubricating oil, which may cause a damage to the vane.
However, in the vane pump having the above-described configuration, when the rotor stops in the state where the diameter direction oil supply hole of the oil supply passage is in communication with the axial direction oil supply groove, the diameter direction gas hole of the gas passage is adapted to communicate with the axial direction gas groove at the same time, so as to allow the air of the outer space to flow into the pump chamber through the gas passage. Hence, since the negative pressure in the pump chamber can be eliminated by allowing the air of the outer space to flow into the pump chamber, a large amount of lubricating oil can be prevented from entering the pump chamber.